This relates generally to flash memories and, particularly, to techniques for thermally treating a flash memory to improve its cycling lifetime.
When flash memories are repeatedly programmed and erased, they may have a tendency to lose data. Cycling of the memory induces the formation of charge traps in an oxide below the floating gate. These charge traps trap electrons during programming and erase operations. These trapped electrons can be released during the storage time of the device. The more the memory is used to recycle, the more trapped electrons may exist and the more prone the device may be to cycling induced failures.
More particularly, after cycling, electrons previously trapped in the tunnel oxide may be released with appropriate activation energy. This mechanism is commonly known as detrapping. The detrapping originates a threshold voltage negative shift so that cells in the so-called zero state move to the read level and can fail. The shift depends on the amount of electrons trapped during cycling, so the higher the quantity of trapped electrons, the higher the threshold shift. The higher the shift, the higher the probability that the stored information will be lost.